1. Field of the Invention
One embodiment of the disclosed invention relates to a method for manufacturing an SOI substrate.
2. Description of the Related Art
In recent years, an integrated circuit using an SOI (silicon on insulator) substrate in which a thin single crystal semiconductor layer is formed on an insulating surface, instead of a bulk silicon wafer, has been developed. The use of an SOI substrate can reduce parasitic capacitance between a drain of a transistor and a substrate; thus, SOI substrates are attracting attention for their ability to improve performance of semiconductor integrated circuits.
One of known methods for manufacturing SOI substrates is a hydrogen ion implantation separation method (for example, see Patent Document 1). A summary of a method for manufacturing an SOI substrate by a hydrogen ion implantation separation method is as follows. First, hydrogen ions are implanted into a silicon wafer by an ion implantation method to form a micro-bubble layer at a predetermined depth from the surface. Next, the silicon wafer into which hydrogen ions have been implanted is bonded to another silicon wafer with a silicon oxide film interposed therebetween. Then, by heat treatment, the micro-bubble layer serves as a cleavage plane and a part of the silicon wafer into which hydrogen ions have been implanted is separated in a thin film shape along the micro-bubble layer. Accordingly, a single crystal silicon film can be formed over the other bonded silicon wafer.
A method for forming a single crystal silicon layer over a base substrate made from glass by using such a hydrogen ion implantation method as described above has been proposed (for example, see Patent Document 2). Since a glass substrate can have a larger area and is less expensive than a silicon wafer, by using a glass substrate as a base substrate, an inexpensive large-sized SOI substrate can be manufactured.
A single crystal semiconductor substrate is irradiated with accelerated hydrogen ions, whereby implantation of the hydrogen ions or doping with the hydrogen ions is performed on the single crystal semiconductor substrate at a predetermined depth to form an embrittled region there. Then, heat treatment is performed. Through the heat treatment, hydrogen contained in the embrittled region is vaporized and further the hydrogen is expanded, so that a cleavage plane is formed in the embrittled region.